White films with a thickness of from 10 to 500 μm are well known. The whiteness of these known films is generally ≦80%. The films also have an undesirable yellow tinge, that is to say they are not brilliant white. The Yellowness Index, which depends on thickness, is >45 for films of thickness from 10 to 100 μm, for example.
The object of the present invention was to provide a white film with a thickness of from 10 to 500 μm which, besides having good orientability, good mechanical properties and good optical properties, above all has a high level of whiteness in combination with a low Yellowness Index.
The good optical properties include uniform, streak-free coloration over the entire width and length of the film, low transparency (≦40%) and an acceptable surface gloss (≧10).
A low Yellowness Index means that according to the invention the Yellowness Index of the films at a film thickness of from 10 to 500 μm is ≦40, preferably ≦35, particularly preferably ≦30.
A high level of whiteness means that the whiteness of the films is ≧85%, preferably ≧87%, in particular ≧90%.
The good mechanical properties include a high modulus of elasticity (EMD>3300 N/mm2; ETD>4800 N/mm2), and also good tear strengths (in MD>130 N/mm2; in TD>180 N/mm2) and good longitudinal and transverse elongations at break (in MD>120%; in TD>70%).
Good orientability includes excellent capabilities of the film for orientation during its production, both longitudinally and transversely, without break-offs.
The novel film should moreover be recyclable, that is to say that any cut material arising during continuous film production can be fed back into the production operation, in particular without loss of optical or mechanical properties from the film.